This invention relates to a method for operating an ultrasonic frequency generating assembly. More particularly, this invention relates to a method for operating such an assembly with pulsed electric power and with automatic frequency control. The method in accordance with the invention is particularly useful for operating an ultrasonic frequency generating assembly for the atomization of a liquid.
European Patent Publication No. 123,277 discloses a method for operating an ultrasonic liquid atomizer wherein the electric energization power is supplied in pulsed form and is on the average sufficient for the adjusted quantity of liquid, while the peak power is so high that any temporary excess of liquid can be shaken off.
Ultrasonic liquid atomizers include electronic frequency generators which must, in general, be manually tuned to their respective fundamental operating frequencies. Ultrasonic atomizers affected by manufacturing tolerances may have different operating frequencies and, therefore, can not be interchanged without adaptation or balancing.
Methods of operating ultrasonic frequency generating assemblies with automatic frequency balancing have been disclosed. However, the ultrasonic generating assemblies with such automatic frequency balancing do not operate with pulsed electric power and do not have a defined operating point or a sufficient safety of operation with respect to the dislodging of a drop of liquid. Moreover, known circuit designs cannot ensure safe or reliable atomizer operation in case of changes in ambient temperature and in generator temperature due to inherent heating. This inability of known circuit designs to compensate for temperature changes arises from the limited trim range of the circuit designs.
An object of the present invention is to provide an improved ultrasonic frequency generating assembly of the above-described type.
Another, more particular, object of the present invention is to provide such an ultrasonic frequency generating assembly with automatic and continuous frequency trimming or adjustment.
Another particular object of the present invention is to provide such an ultrasonic frequency generating assembly which enables a reliable liquid atomization with automatic clearing of a flooded atomizer plate.
Further objects of the present invention are to provide such an ultrasonic frequency generating assembly which has low power consumption, low thermal stress and a high atomization rate.
Yet a further object of the present invention is to provide such an ultrasonic frequency generating assembly with automatic temperature monitoring.